SAFE SEX ADVICE PLS

Em
Hello everyone, I hope you're doing all good. I come here to ask for some help. I know you'll help me. I've struggled with obsessive compulsive disorder since I was a little girl and it's become something that makes my life unbearable. I'm so scared about everything, I can't do anything without being worried and over worrying for weeks. I got so worried about an exam that my period hasn't come yet. 
Tonight I took an ovulation test as I want to have my first time with my boyfriend. We're going to use condoma and even though I know my period is going to start soon and that I  not ovulating right now I still think I might get pregnant and it sucks to worry so much that I can't even enjoy the fact that it's my first time with the person I love. Please help me out. What can I do to calm myself? Or better said, to have safe enough sex?